Highly flowable propylene block copolymers

ABSTRACT

The invention relates to highly flowable propylene block copolymers that comprise 50 to 80 wt.-% of a propylene homopolymer and 10 to 70 wt.-% of a propylene copolymer having 5 to 50 wt.-% of a C 2 -C 8  alk-1-ene polymerized into it that is different from propylene, and that are obtainable from the gaseous phase by a two-step polymerization by means of a Ziegler-Natta catalyst system. In a first polymerization step, the propylene is polymerized at a pressure of 10 to 50 bar, a temperature of 50 to 100° C. and an average dwelling time of the reaction mixture of 0.3 to 5 hours in the presence of at least 2.0% by volume, based on the total volume, of hydrogen. The propylene homopolymer obtained in said first polymerization step is transferred together with the Ziegler-Natta catalyst system into an intermediate container, expanded for 0.01 to 5 minutes to less than 5 bar and maintained at a temperature of 10 to 80° C. The pressure in the intermediate container is then increased by 5 to 60 bar by introducing under pressure a gaseous mixture, and the propylene homopolymer is then transferred to a second polymerization step together with the Ziegler-Natta catalyst system. In said second polymerization step, a mixture from propylene and a C 2 -C 8  alkylene is polymerized into the propylene homopolymer at a pressure of 10 to 50 bar, a temperature of 50 to 100° C. and an average dwelling time of 0.5 to 5 hours. The weight ratio between the monomers reacted in the first and those reacted in the second polymerization step are adjusted to be in the range of from 4:1 to 1:1.

The present invention relates to highly flowable propylene blockcopolymers, comprising 50 to 80 wt.-% of a propylene homopolymer and 20to 50 wt.-% of a propylene copolymer, with 10 to 70 wt.-% of a C₂-C₈1-alkene other than propylene polymerized into to it, this 1-alkenebeing obtainable by two-stage polymerization by means of a Ziegler-Nattacatalyst system from the gas phase; in a first polymerization stage,propylene is polymerized at a pressure of 10 to 50 bar, a temperature of50 to 100° C., and a mean dwell time of the reaction mixture of 0.3 to 5hours in the presence of at least 2.0 vol.-% of hydrogen in proportionto the total volume, and then the propylene homopolymer obtained in thefirst polymerization stage is introduced along with the Ziegler-Nattacatalyst system into an intermediate container, where it is firstdepressurized for 0.1 to 5 minutes to less than 5 bar and maintained ata temperature of 10 to 80° C., and then, by the introduction underpressure of a gas mixture, the pressure in the intermediate container israised again by 5 to 60 bar, and the propylene homopolymer along withthe Ziegler-Natta catalyst system is thereupon transferred to a secondpolymerization stage, where a mixture of propylene and a C₂-C₈ 1-alkeneis added by polymerization to the propylene homopolymer at a pressure of10 to 50 bar, a temperature of 50 to 100° C., and a mean dwell time of0.5 to 5 hours, and the weight ratio between the monomers converted inthe first and second polymerization stages, respectively, is adjusted tobe is in the range of 4:1 to 1:1.

The present invention also relates to a method for producing highlyflowable propylene block copolymers of this kind and to their use asfilms, fibers or molded bodies.

Propylene ethylene block copolymers obtainable by polymerization withZiegler-Natta catalysts have already been described in numerous patents(U.S. Pat. Nos. 4,454,299 and 4,455,405, and German Patents DE-A 3 827565 and DE-A 4 004 087). Such block copolymers are typically produced bya method in which first gaseous propylene is polymerized in a firstpolymerization stage, and the propylene homopolymer obtained from it isthen brought to a second polymerization stage, where a mixture ofpropylene and ethylene is added to it by polymerization. The method isconventionally performed at elevated pressure and in the presence ofhydrogen as a molar mass regulator. The propylene ethylene blockcopolymers obtainable by this method usually have good impact strengthand rigidity.

Propylene block copolymers that have a high proportion of rubber, thatis, block copolymers in which the copolymer obtained in the secondpolymerization stage represents a high proportion of the total blockcopolymer, can be obtained directly from the reactor, by the usualpolymerization methods, only for relatively low melt flow rates. This isdue, among other factors, to the fact that the high concentrations ofhydrogen required to regulate the molar masses of the block copolymersare often not feasible in practical terms. Moreover, in the productionof block copolymers with a high proportion of rubber and a relativelyhigh melt flow rate, unwanted plating out is observed in the secondpolymerization stage, which is associated with problems of morphology ofthe products obtained. For these reasons, from a process standpoint itis quite difficult to produce rubber-rich propylene block copolymersthat have both high impact strength and high flowability, or in otherwords whose melt flow rates have high values.

One possibility of producing rubber-rich propylene block copolymers thathave high flowability is for rubber-rich propylene block copolymers tobe subjected to a subsequent molar mass reduction with the aid oforganic peroxides, as a result of which their melt flow rate and hencetheir flowability can be increased markedly. However, this kind of molarmass reduction requires a relatively complicated additional method step.Moreover, the use of organic peroxides has a number of disadvantages,among them increased emissions of low-molecular components, annoyingodor, and sacrifices in terms of rigidity, thermostability, andsoftening behavior.

It was therefore the object of the present invention to overcome thedisadvantages described and to develop highly flowable propylene blockcopolymers with a high rubber content which can be produced simply andwithout the use of peroxides, and which are distinguished, among otherproperties, by high impact strength and rigidity and goodthermostability and flowability in the injection-molding field, andwhich moreover have only slight proportions of highly volatilecomponents.

Accordingly, the novel highly flowable propylene block copolymersdefined at the outset were discovered.

The propylene block copolymers of the invention comprise 50 to 80 wt.-%,and in particular 60 to 80 wt.-%, of a propylene homopolymer and 20 to50 wt.-%, in particular 20 to 40 wt.-%, of a propylene copolymer, with10 to 70 wt.-%, refer to the propylene copolymer, of a C₂-C₈ 1-alkeneother than propylene that is added to it by polymerization. Theproportion of C₂-C₈ 1-alkene polymerized into the propylene copolymer isin particular 20 to 60 wt.-%.

The term “C₂-C₈ 1-alkenes” is understood to mean linear and branched1-alkenes, in particular ethylene, 1-butene, 1-pentene, 1-hexene,1-heptene or 1-octene, as well as mixtures of these comonomers, withethylene or 1-butene being used preferentially.

The propylene block copolymers of the invention can be obtained bytwo-stage polymerization from the gas phase.

The polymerization in both stages is effected by means of aZiegler-Natta catalyst system. In particular, catalyst systems are usedof the kind that besides a) a titanium-containing solid component alsohave b) cocatalysts in the form of organic aluminum compounds and c)electron donor compounds. The propylene block copolymers of theinvention can be obtained in this way.

For producing the titanium-containing solid component (a), the halidesor alcoholates of trivalent or quadrivalent titanium are used astitanium compounds; titanium alkoxy halogen compounds or mixtures ofvarious titanium compounds can also be considered. Preferably, thetitanium compounds that contain chlorine as the halogen are used. Alsopreferred are the titanium halides, which besides titanium contain onlyhalogen, and above all, the titanium chlorides and in particulartitanium tetrachloride.

The titanium-containing solid component (a) preferably contains at leastone halogen-containing magnesium compound. Halogens are understood hereto mean chlorine, bromine, iodine, or fluorine; bromine or in particularchlorine are preferred. The halogen-containing magnesium compounds areeither used directly in the production of the titanium-containing solidcomponent (a) or are formed in the production thereof. As magnesiumcompounds that are suitable for producing the titanium-containing solidcomponent (a), the magnesium halides can be considered above all, suchas magnesium dichloride or magnesium dibromide in particular, ormagnesium compounds from which the halides can be obtained in the usualway, for instance by reaction with halogenating agents, such asmagnesium alkyls, magnesium aryls, magnesium alkoxy compounds, ormagnesium aryloxy compounds, or Gridnard compounds. Preferred examplesof halogen-free compounds of magnesium that are suitable for producingthe titanium-containing solid component (a) are n-butylethylmagnesium orn-butyloctylmagnesium. Preferred halogenation agents are chlorine orhydrogen chloride. However, titanium halides can also be used ashalogenation agents.

Moreover, the titanium-containing solid component (a) expedientlycontains electron donor compounds, such as mono- or polyfunctionalcarboxylic acids, carboxylic acid anhydrides or carboxylic acid esters,and moreover ketones, ether, alcohols, lactones, or organic phosphorousor silicon compounds.

As the electron donor compounds within the titanium-containing solidcomponent, carboxylic acid derivatives and in particular phthalic acidderivatives of the general formula (II)[paste in (II)]are preferably used, in which formula X and Y each stand for onechlorine or bromine atom or a C₁-C₁₀ alkoxy radical, or jointly standfor oxygen in the anhydride function. Especially preferred electrondonor compounds are phthalic acid esters, in which X and Y stand for aC₁-C₈ alkoxy radical. Examples of phthalic acid esters that arepreferably used are diethyl phthalate, di-n-butyl phthalate, diisobutylphthalate, di-n-pentyl phthalate, di-n-hexyl phthalate, di-n-heptylphthalate, di-n-octyl phthalate, or di-2-ethylhexyl phthalate.

Other preferred electron donor compounds within the titanium-containingsolid component are diesters of 3- or 4-unit, optionally substituted,cycloalkyl-1,2-dicarboxylic acids, as well as monoesters of substitutedbenzophenone-2-carboxylic acids, or substitutedbenzophenone-2-carboxylic acids. In these esters, the usual alkanols inesterification reactions are used as the hydroxy compounds, such asC₁-C₁₅ alkanols or C₅-C₇ cycloalkanols, which in turn can have one ormore C₁-C₁₀ alkyl groups, as well as C₆-C₁₀ phenols.

Mixtures of various electron donor compounds can also be used.

In the production of the titanium-containing solid component (a), as arule per mol of the magnesium compound, from 0.05 to 2.0 mol, andpreferably from 0.2 to 1.0 mol, of the electron donor compounds areused.

Furthermore, the titanium-containing solid component (a) can containinorganic oxides as a vehicle. As a rule, a fine-particle inorganicoxide is used as the vehicle, which has a mean particle diameter of 5 to200 μm, and preferably 20 to 70 μm. The term “mean particle diameter” isunderstood here to mean the volume-related mean value (median value) ofthe particle-size distribution determined by Coulter counter analysis.

Preferably, the particles of the fine-particle inorganic oxide arecomposed of primary particles that have a mean particle diameter of theprimary particles of from 1 to 20 μm and in particular from 1 to 5 μm.The so-called primary particles are porous, granular oxide particles,which are generally obtained by grinding up a hydro gel of the inorganicoxide. It is also possible for the primary particles to be sieved beforethey are further processed.

The inorganic oxide that is preferably used is also characterized byhaving voids or channels with a mean diameter of 0.1 to 20 μm, inparticular 1 to 15 μm, whose macroscopic volumetric proportion of thetotal particles is in the range from 5 to 30% and in particular in therange from 10 to 30%.

The determination of the mean particle diameter of the primary particlesand of the macroscopic volumetric proportion of the voids and channelsin the inorganic oxide is expediently effected by image analysis, usingscanning electron microscopy, or electron probe microanalysis, in eachcase at particle surfaces and particle cross sections of the inorganicoxide. The pictures obtained are evaluated, and from that the meanparticle diameter of the primary particles and the macroscopicvolumetric proportion of the voids and channels are determined. Theimage analysis is preferably done by converting the electron microscopicdata material into a gray-value binary image and by digital evaluationusing a suitable electronic data processing program, such as thesoftware analysis package produced by the corporation known as SIS.

The inorganic oxide to be preferably used can be obtained for instanceby spray drying the ground hydro gel, which for that purpose is mixedwith water or an aliphatic alcohol. Such fine-particle inorganic oxidesare also available in commerce.

The fine-particle inorganic oxide furthermore typically has a porevolume of 0.1 to 10 cm³/g, preferably 1.0 to 4.0 cm³/g, and a specificsurface area of 10 to 1000 m²/g, preferably 100 to 500 m²/g; thesevalues are understood to be determined by mercury porosimetry under DIN66133 and nitrogen adsorption under DIN 66131.

It is also possible to use an inorganic oxide whose pH value, that is,the negative base-10 logarithm of the proton concentration, is in therange from 1 to 6.5 and in particular in the range from 2 to 6.

As inorganic oxides, above all the oxides of silicon, aluminum,titanium, or one of the metals of the first or second primary group ofthe periodic system can be considered. As a particularly preferredoxide, besides aluminum oxide or magnesium oxide or a layer silicate,silicon oxide (silica gel) is used above all. Mixed oxides can also beused, such as aluminum silicates or magnesium silicates.

The inorganic oxides used as the vehicle contain water on their surface.This water is bonded, partly physically by adsorption and partlychemically in the form of hydroxyl groups. By thermal or chemicaltreatment, the water content of the inorganic oxide can be reduced oreliminated entirely; as a rule, in a chemical treatment, typical dryingagents are used, such as SiCl₄, chlorosilane, or aluminum alkyls. Thewater content of suitable inorganic oxides amounts to from 0 to 6 wt.-%.Preferably, an inorganic oxide is used without further treatment, in theform in which it is available in commerce.

The magnesium compound and the inorganic oxide within thetitanium-containing solid component (a) are preferably present in suchquantities that, per mol of the inorganic oxide, from 0.1 to 1.0 mol, inparticular from 0.2 to 0.5 mol, of the compound of magnesium arepresent.

In the production of the titanium-containing solid component (a), C₁ toC₈ alkanols, such as methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, isobutanol, n-hexanol, n-heptanol,n-octanol, or 2-ethylhexanol, or mixtures thereof, are also used as arule. Preferably, ethanol is used.

The titanium-containing solid component can be produced by methods knownper se. Examples are described, among others, in European PatentDisclosures EP-A 45 975, EP-A 45 977, EP-A 86 473, and EP-A 171 200, aswell as British Patent GB-A 2 111 066, and US Patents 4,857,613 and5,288,824. Preferably, the method known from German Patent DisclosureDE-A 195 29 240 is employed.

Suitable aluminum compounds (b), besides trialkylaluminum, are alsocompounds of the kind in which one alkyl group is replaced with analkoxy group or a halogen atom, such as chlorine or bromine. The alkylgroups may be identical to one another or different. Linear or branchedalkyl groups can be considered. Preferably, trialkylaluminum compoundsare used, whose alkyl groups each have from 1.8 carbon atoms, examplesbeing trimethylaluminum, triethylaluminum, triisobutylaluminum,trioctylaluminum, or methyldiethylaluminum, or mixtures thereof.

In addition to the aluminum compound (b), as a rule electron donorcompounds (c) are used as further cocatalysts, such as mono- orpolyfunctional carboxylic acids, carboxylic acid anhydrides orcarboxylic acid esters, and also ketones, ether, alcohols, lactones, andorganic phosphorous and silicon compounds; the electron donor compounds(c) may be the same as or different from the electron donor compoundsused for producing the titanium-containing solid component (a).Preferred electron donor compounds are organic silicon compounds of thegeneral formula (I)R¹ _(n)Si(OR²)_(4-n)   (I),in which R¹ is the same or different and stands for a C₁-C₂₀ alkylgroup, a 5- to 7-unit cycloalkyl group, which in turn can be substitutedwith a C₁-C₁₀ alkyl, a C₆-C₁₈ aryl group, or a C₆-C₁₈ aryl-C₁-C₁₀ alkylgroup; R² is the same or different and stands for a C₁-C₂₀ alkyl group,and n stands for the whole numbers 1, 2 or 3. Especially preferably,compounds in which R¹ stands for a C₁-C₈ alkyl group or a 5- to 7-unitcycloalkyl group, and R² stands for a C₁ to C₄ alkyl group, and n standsfor the numbers 1 or 2.

Among these compounds, dimethoxydiisopropylsilane,dimethoxyisobutylisopropylsilane, dimethoxydiisobutylsilane,dimethoxydicyclopentylsilane, dimethoxyisopropyl-tert-butylsilane,dimethoxyisobutyl-sec-butylsilane, anddimethoxyisopropyl-sec-butylsilane can be emphasized in particular.

Preferably, the cocatalysts (b) and (c) are used in a quantity such thatthe atomic ratio between aluminum from the aluminum compound (b) andtitanium from the titanium-containing solid component (a) amounts tofrom 10:1 to 800:1, in particular from 20:1 to 200:1, and the molarratio between the aluminum compound (b) and the electron donor compound(c) amounts to from 1:1 to 250:1, and in particular from 10:1 to 80:1.

The titanium-containing solid component (a), the aluminum compound (b),and the electron donor compound (c) that is as a rule used together formthe Ziegler-Natta catalyst system. The catalyst ingredients (b) and (c)can be introduced into the polymerization reactor either together withthe titanium-containing solid component (a), or as a mixture, orindividually in an arbitrary order.

The method for producing the highly flowable propylene block copolymersof the invention is performed in two successive polymerization stages,that is, in a reactor cascade, in the gas phase. The usual reactors usedfor the polymerization of C₂-C₈ 1-alkenes can be used. Suitable reactorsinclude among others continuous stirred tanks, loop reactors, orfluidized bed reactors. The size of the reactors is not of particularimportance for the method of the invention. It depends on the outputthat is to be attained in the reaction zone or in the individualreaction zones.

As the reactors, both fluidized bed reactors and horizontally orvertically stirred powdered bed reactors are used in particular. In themethod that is also according to the invention, the reaction bedgenerally comprises the polymer of C₂-C₈ 1-alkenes that is polymerizedin the applicable reactor.

In an especially preferred embodiment, the method used to produce thepropylene block copolymers of the invention is performed in a cascade ofreactors connected in series with one another, in which the powderedreaction bed is kept in motion by a vertical stirrer; so-called freelysupported helical stirrers are especially suitable. Such stirrers areknown for instance from European Patent Disclosures EP-B 000 512 andEP-B 031 417. They are distinguished in particular in that theydistribute the powdered reaction bed quite homogeneously. Examples ofsuch powdered reaction beds are described in EP-B 038 478. The reactorcascade preferably comprises two series-connected tanklike reactors,provided with a stirrer and with a volumetric content of from 0.1 to 100m³, such as 12.5, 25, 50 or 75 m³.

In the polymerization for producing the propylene block copolymers ofthe invention, their molar mass can be monitored and adjusted by meansof the usual regulators in polymerization technology, such as hydrogen.Besides regulators so-called regulatory agents can be used, that is,compounds that vary the catalyst activity, or antistatic agents. Theselatter agents prevent plating out on the wall that could be caused byelectrostatic charging.

In the first polymerization stage, for producing the propylene blockcopolymers of the invention, under the usual reaction conditions,propylene is polymerized at a pressure of 10 to 50 bar, in particular 15to 40 bar, a temperature of 50 to 100° C., in particular 60 to 90° C.,and a mean dwell time of 0.3 to 5 hours, in particular 0.8 to 4 hours.For regulating the molar mass of the propylene homopolymer obtained, thepolymerization in the first polymerization stage is done in the presenceof at least 2.0 vol.-%, and in particular at least 5.0 vol.-%, ofhydrogen, referred to the total mixture present in the polymerizationstage. The propylene homopolymer obtained in the first polymerizationstage forms the so-called matrix for the propylene block copolymers ofthe invention and has a polydispersion index (PI) of preferably at least2.8 and in particular at least 3.0.

Next, the propylene homopolymer obtained in the first polymerizationstage, with the Ziegler-Natta catalyst system used, is removed from thefirst polymerization stage and transferred into an intermediatecontainer. As the intermediate containers, the reactors or containerstypically used for the polymerization of C₂-C₈ 1-alkenes are used.Suitable intermediate containers are for instance cylindrical tanks,stirring vessels, or cyclones.

In the intermediate container, the propylene homopolymer discharged fromthe first polymerization stage, together with the Ziegler-Natta catalystsystem, is first depressurized for 0.1 to 5 minutes, in particular 0.2to 4 minutes, to less than 5 bar, and preferably to less than 3.5 bar.During this period of time, per kg of the propylene homopolymer, 0.001 gto 10 g, in particular 0.001 g to 1.0 g of a C₁-C₈ alkanol can be addedto the propylene homopolymer, for better regulation of the furtherpolymerization step. Isopropanol is especially suited for this purpose,but ethanol or glycol is also suitable. The intermediate container isfirst maintained at a temperature of 10 to 80° C., in particular 20 to70° C., and then, by introducing a gas mixture of the monomers used,that is, propylene and the C₂-C₈ 1-alkenes, under pressure, the pressurein the intermediate container is again raised by from 5 to 60 bar, andin particular by from 10 to 50 bar. In the intermediate container, thereaction mixture can also be reacted with conventional antistaticagents, such as polyglycol ether from fatty alcohols, fatty acids, andalkyl phenols, alkyl sulfates, and alkyl phosphates, as well asquaternary ammonium compounds.

After that, the propylene homopolymer, together with the Ziegler-Nattacatalyst system, is discharged from the intermediate container andintroduced into the second polymerization stage. In the secondpolymerization stage, a mixture of propylene and a C₂-C₈ 1-alkene isthen added by polymerization to the propylene homopolymer, at a pressureof 10 to 50 bar, in particular 10 to 40 bar, a temperature of 50 to 100°C., in particular 60 to 90° C., and a mean dwell time of 0.5 to 5 hours,in particular 0.8 to 4 hours. The weight ratio between the monomersreacted in the first polymerization stage and the monomers reacted inthe second polymerization stage is adjusted to be in the range of 4:1 to1:1, in particular in the range from 4:1 to 1.5:1. As in theintermediate container, in the second polymerization stage as well, perkg of propylene copolymer, from 0.001 g to 10 g, in particular 0.005 gto 0.5 g of a C₁-C₈ alkanol can be added. For this purpose, isopropanol,glycol or ethanol is especially recommended. Suitable comonomers of thepropylene in the second polymerization stage include among othersethylene and 1-butene. The proportion of the comonomer or comonomers ofthe propylene in the total gas mixture in the second polymerizationstage is preferably from 15 to 60 vol.-%, in particular 20 to 50 vol.-%.

The propylene block copolymers of the invention obtained in this wayhave a melt flow rate (MFR), at 230° C. and at a weight of 2.16 kg,under ISO 1133, that satisfies the following equation (I):MFR≧101.39+0.0787*XS ²−5.4674*XS,   (I)in which XS stands for the proportion of propylene copolymer formed inthe second polymerization stage, in percent, referred to the totalpropylene block copolymer.

The melt flow rate (MFR) of the propylene block copolymers obtained isas a rule in the range from 2 to 100 g/10 min, in particular in therange from 5 to 80 g/10 min, in each case at 230° C. and at a weight of2.16 kg. The melt flow rate corresponds to the quantity of polymer thatis expressed within 10 minutes from the test apparatus, standardizedunder ISO 1133, at a temperature of 230° C. and at a weight of 2.16 kg.The propylene block copolymers of the invention are produced withoutmolar mass reduction by peroxides.

The propylene block copolymers of the invention are distinguished, amongother properties, by high flowability, that is, an elevated melt flowrate, with simultaneously markedly increased rubber proportions, whichmeans that the proportion of the propylene copolymer in the totalpropylene block copolymer is increased. The propylene block copolymersof the invention are furthermore characterized by high impact resistanceand rigidity as well as by good thermostability and flowability ininjection molding (spiral flow). Furthermore, they contain onlyrelatively little of low-molecular ingredients, such as n-heptane ortert-butanol.

The method that is also according to the invention can be performed in asimple way in the usual reactors in plastics technology, without havingto subject the propylene block copolymers obtained to a further molarmass reduction.

The propylene block copolymers of the invention are suitable above allfor producing films, fibers and molded bodies.

EXAMPLES

In all the examples 1, 2 and 3 of the invention, and the comparisonexamples A, B and C, a Ziegler-Natta catalyst system was used thatcontained a titanium-containing solid component (a) produced by thefollowing method.

In a first stage, a fine-particle silica gel, which had a mean particlediameter of 30 μm, a pore volume of 1.5 cm³/g, and a specific servicearea of 260 m²/g, was mixed with a solution of n-butyloctylmagnesium inn-heptane; per mol of SiO₂, 0.3 mol of the magnesium compound was used.The fine-particle silica gel was additionally characterized by a meanparticle size of the primary particles of the 3 to 5 um and by voids andchannels with a diameter of 3 to 5 μm; the macroscopic volumetricproportion of the voids and channels in the total particles wasapproximately 15%. The solution was stirred for 45 minutes at 95° C.,then cooled down to 20° C., after which ten times the molar amount,referred to the organic magnesium compound, of hydrogen chloride wasintroduced. After 60 minutes, the reaction product was mixed, stirringconstantly, with 3 mol of ethanol per mol of magnesium. This mixture wasstirred for 0.5 hours at 80° C. and then mixed with 7.2 mol of titaniumtetrachloride and 0.5 mol of di-n-butyl phthalate, in each case referredto 1 mol of magnesium. Stirring was then done for 1 hour at 100° C., andthe solid material thus obtained was filtered off and washed multipletimes with ethylbenzene.

The solid product obtained from this was extracted for 3 hours at 125°C. with a 10 vol.-% solution of titanium tetrachloride in ethylbenzene.After that, the solid product was separated from the extraction agent byfiltration and washed with n-heptane until the extraction agentcontained only 0.3 wt.-% of titanium tetrachloride.

The titanium-containing solid component (a) contained

-   -   3.5 wt.-% Ti    -   7.4 wt.-% Mg    -   28.2 wt.-% Cl.

Besides the titanium-containing solid component (a), triethylaluminumand dimethoxyisobutylisopropylsilane were used as cocatalysts, inaccordance with the teaching of U.S. Pat. Nos. 4,857,613 and 5,288,824.

Examples 1, 2 and 3

In all the examples 1, 2 and 3 of the invention, the method wasperformed in two series-connected stirring autoclaves, equipped with afreely supported helical stirrer, each with a useful volume of 200 L.Both reactors contained a solid bed in motion of fine-particle propylenepolymer.

In the first polymerization reactor, the propylene was introduced ingaseous form and polymerized at a mean dwell time, pressure andtemperature as indicated in Table I. The Ziegler-Natta catalyst systemused comprised the titanium-containing solid component (a), as well astriethylaluminum and isobutylisopropyldimethoxysilane as cocatalysts.The metered dosage of the solid component described was adjusted suchthat the transfer from the first to the second polymerization reactor isequivalent on average over time to the values shown in Table I. Themetered dosage of this component was made with the fresh propylene addedto regulate the pressure. Also added by metered dosage to the reactorwere: triethylaluminum (in the form of a 1-molar heptane solution), in aquantity of 60 to a maximum of 105 ml/h, andisobutylisopropyldimethoxysilane (in the form of a 0.125 molar heptanesolution), in a quantity of 70 to a maximum of 120 ml/h, as furthercatalyst components. To regulate the melt flow rate (under ISO 1133),hydrogen was added in metered form; the concentration of hydrogen in thereaction gas was monitored by gas chromatography.

Polymer granulate was removed successively from the reactor by brieflydepressurizing the reactor via an immersion tube. The propylenehomopolymer formed in the first reactor was as a result introduceddiscontinuously with the catalyst into an intermediate container, whereit was mixed with isopropanol (in the form of a 0.5-molar heptanesolution). The metered quantity of isopropanol added was adjusted suchthat the weight ratio between the propylene homopolymer obtained in thefirst reactor and the propylene copolymer produced in the second reactorachieves the values shown in Table I below. The quantity of isopropanolused can also be divided, in such a way that it is metered partly intothe intermediate container and partly into the second reactor. In theintermediate container, the pressure in each case was lowered to 1 barand maintained for 30 seconds, and then raised to 30 bar by introductionof a gas mixture under pressure, the gas mixture being equivalent to thecomposition in the second reactor.

The polymer powder was then introduced discontinuously from theintermediate container into the second reactor. There, a mixture ofpropylene and ethylene was added by polymerization to it at a totalpressure, temperature and mean dwell time as shown in Table I. Theproportion of ethylene in each case was approximately 30 vol.-%. Theweight ratio between the propylene homopolymer formed in the firstreactor and the propylene copolymer formed in the second reactor wasmonitored with the aid of the isopropanol added and is shown in Table 1.

The precise conditions in the examples 1, 2 and 3 of the invention, thatis, the values for pressure, temperature and dwell time, the quantity ofhydrogen used, and the quantity of cocatalysts used, the melt flow rate(MFR), and the transfer amount, that is, the quantity of each polymerobtained, are each shown for both polymerization reactors in Table Ibelow. Table I also shows the weight ratio between the propylenehomopolymer [PP (I)] formed in the first polymerization reactor and thepropylene ethylene copolymer [EPR (II)] obtained in the secondpolymerization reactor.

The proportion of the propylene ethylene copolymer formed in the secondreactor is calculated from the transfer and discharge amounts asfollows: ${\%\quad{of}\quad{copolymer}} = \frac{\begin{matrix}{{{discharge}\quad\left( {{second}\quad{reactor}} \right)} -} \\{{transfer}\quad\left( {{first}\quad{reactor}} \right)}\end{matrix}}{{{discharge}\quad\left( {{second}\quad{reactor}} \right)}\quad}$

The properties of the products obtained are summarized, together withthe comparison examples (comparison examples 1′, 2′ and 3′) in TablesIII, IV and V. TABLE I Example 1 Example 2 Example 3 Reactor I Pressure(I) [bar] 32 32 22 Temperature (I) [° C.] 80 80 70 Hydrogen (I) [vol.-%] 10.9 9.5 6.3 Quantity of isobutylisopropyl- 103 120 70dimethoxysilane (0.125 mol) [ml/h] Quantity of 90 105 60triethylaluminum (1 mol) [ml/h] Dwell time (I) [h] 1.5 1.3 2.3 MFR (I)[g/10 min] 190 180 **5 Transfer [kg/h] 30 35 *9 Reactor II Pressure (II)[bar] 15 18 22 Temperature (II) [° C.] 70 70 70 Hydrogen (II) [vol.- %]1.5 1.2 0.9 Ethylene [vol.- %] 30.6 29.4 29.4 Dwell time (II) [h] 1.21.0 1.1 Output [kg/h] 38.6 46.8 42.9 MFR (II) [g/10 min] 51 31 7.5Weight ratio PP (I):EPR (II) 4:1 3.3:1 2:1

Comparison Examples 1′, 2′ and 3′

In all the comparison examples 1′, 2′ and 3′, the method was performedin two series-connected stirring autoclaves, equipped with a freelysupported helical stirrer, each with a useful volume of 200 L. Bothreactors contained a solid bed in motion of fine-particle propylenepolymer.

In the first polymerization reactor, the propylene was introduced ingaseous form and polymerized at a mean dwell time of 2.3 hours, with theaid of a Ziegler-Natta catalyst comprising the titanium-containing solidcomponent (a), triethylaluminum and isobutylisopropyldimethoxysilane, ata pressure and temperatures as shown in Table II. The metered dosage ofthe solid component described was adjusted such that the transfer fromthe first to the second polymerization reactor is equivalent on averageto the values shown in Table II. The metered dosage of this componentwas made with the fresh propylene added to regulate the pressure.Triethylaluminum (in the form of a 1-molar heptane solution), in aquantity of 60 ml/h, and 72 ml/h of isobutylisopropyldimethoxysilane (inthe form of a 0.125 molar heptane solution), were also added to thereactor in metered form, as further catalyst components. For regulatingthe melt flow rate (under ISO 1133), hydrogen was added in metered form;the concentration of hydrogen in the reaction gas was monitored by gaschromatography.

Polymer granulate was removed successively from the reactor by brieflydepressurizing the reactor via an immersion tube. The propylenehomopolymer formed in the first reactor was as a result introduceddiscontinuously with the catalyst and introduced together with unreactedmonomers into the second reactor, but without depressurizing this in anintermediate container.

There, a mixture of propylene and ethylene was added by polymerization,at a total pressure, temperature and mean dwell time as shown in TableII. The proportion of ethylene in each case was approximately 30 vol.-%.The weight ratio between the propylene homopolymer [PP (I)] formed inthe first reactor and the propylene copolymer [EPR (II)] formed in thesecond reactor is shown in Table II. Also added in metered form to thesecond reactor was isopropanol (in the form of a 0.5 molar heptanesolution). The quantity of isopropanol added in metered form wasadjusted such that the weight ratio between PP (I) and EPR (II) shown inTable II was maintained.

The propylene block copolymers obtained in comparison examples 1′, 2′and 3′ were then, after a molar mass reduction with peroxides using a 5wt.-% solution of di-tert-butylperoxide in n-heptane (Luperox® 101, madeby Interox/Peroxid-Chemi) in a double worm extruder (ZSK 30, Worm 8 A,made by Werner & Pfleiderer). In this way, it was possible to increaseits melt flow rate (MFR) markedly. The melt flow rates before (MFR II)and after the molar mass reduction (MFR after reduction) are shown inTable II below. TABLE II Comparison Comparison Comparison Example 1′Example 2′ Example 3′ Reactor I Pressure (I) [bar] 32 32 22 Temperature(I) [° C.] 80 80 80 Hydrogen (I) [vol.- %] 0.4 0.9 0.4 Quantity ofisobutylisopropyl- 72 72 72 dimethioxysilane (0.125 mol) [ml/h] Quantityof triethylaluminum 60 60 60 (1 mol) [ml/h] Dwell time (I) [h] 2.3 2.32.3 MFR (I) [g/10 min] 3.5 16 15 Transfer [kg/h] 20 20 20 Reactor IIPressure (II) [bar] 15 15 23 Temperature (II) [° C.] 70 70 70 Vol.- %hydrogen (II) 1.6 3.8 2.1 [vol.- %] Vol- % ethylene [vol.- %] 30 30 30Dwell time (II) [h] 1.8 1.8 1.5 Output [kg/h] 25 26.8 30.2 MFR (II)[g/10 min] 2 7.5 3.5 MFR after reduction 48 31 7 [g/10 min] Weight ratio4:1 3:1 2:1 PP(I):EPR(II)

In Tables III, IV and V that follow, the results of measurements of thepropylene block copolymers, obtained in examples 1, 2 and 3 of theinvention, are compared with measurements made for propylene blockcopolymers not according to the invention, in the comparison examples1′, 2′ and 3′. The following properties were measured: Properties:Method XS (xylene solubles): ASTM D5492-98 Standard Test Method forDetermination of Xylene Solubles in Propylene Plastics Limit viscosityof rubber As the so-called rubber phase, phase (propylene copolymer):the combined fractions of a TREF fractionation were used, which wereeluted at temperatures below 80° C. in xylene. The determination of thelimit viscosity was done in decalin at 135° C. in accordance with ISO1628. MFR (I); MFR (II); MFR ISO 1133, 230° C., 2.16 kg (afterreduction) [g/10 min]: Crossover module and poly- ISO 6721-10; as thematrix, the dispersion index (PT) of the combined fractions of a TREFpropylene homopolymer fractionation were defined, (matrix) which areeluted at temperatures above 90° C. in xylene. Apparatus: RDS2 withplate/plate geometry, diameter = 25 mm, amplitude = 0.05-1, preheatingtime = 5-10 min, T = 170-220° C. Determination of the P1 value: PI =54.6 × (modulus separation)^(−1.76)${{modulus}\quad{separation}} = \frac{\left( {G^{\prime} = {500\quad{Pa}}} \right)^{\upsilon}}{\left( {G^{''} = {500\quad{Pa}}} \right)^{\upsilon}}$γ= frequency Spiral flow: ISO 1133, peak pressure 100 bar, T = 250° C.Vicat A temperature: ISO 306, VST A50 Thermostability B: ISO 75-2 (120 ×10 × 4 mm) TREF fractionation: per L. Wild, Temperature rising elutionfractionation, Adv. Polym. Sci. 98, 1-47 (1990). Fractions were elutedwith xylene at 40, 80, 90, 100, 120 and 125 C. Volatile components,Head-space gas chromatography, oligomers, proportions of 60 m DB-1, film1 μm, specimen tert-butanol and n-heptane: weight: 1 g; scavenging gas:He, tempering: 1 h at 120° C., evaluation: mass proportion in ppm, ext.standard. Modulus of elasticity and DIN 53457 tension: Impact bendingtest (ack) ISO 179-2/1eA (F); ISO 179- at 0° C. and 23° C.: 2/1eU

TABLE III Comparison Example 1 Example 1′ MFR (I)/MFR (II)/ 190/51/513.5/2/48 MFR (after reduction) XS [%] 21 21.1 Modulus of elasticity 11261051 [MPa] ack (23° C.) [kJ/m²] 7.8 7.5 ack (0° C.) [kJ/m²] 5.6 5.8Spiral flow [cm] 113 97 Thermostability B [° C.] 87 77 Vicat A [° C.]144 140 P.I., matrix 3.19 2.59 Crossover module, matrix 16,000 35,800[Pa] Limit viscosity rubber 3.73 dl/g 1.67 dl/g [^(n) _(rubber), dl/g]Proportion of tert- <1 ppm  4 ppm butanol [ppm] Proportion of n-heptane15 ppm 647 ppm [ppm]

TABLE IV Comparison Example 2 Example 2′ MFR (I)/MFR (II)/ 180/31/3116/7.5/31 MFR (after reduction) XS [%] 23 22 Modulus of elasticity 10371074 [MPa] ack (23° C.) [kJ/m²] 10.2 7.2 ack (0° C.) [kJ/m²] 6.5 5.6Spiral flow [cm] 101 92 Thermostability B [° C.] 81 74 Vicat A [° C.]142 140 P.I., matrix 3.17 2.52 Crossover module, matrix 7,000 34,100[Pa] Limit viscosity rubber 3.98 dl/g 1.68 dl/g [^(n) _(rubber), dl/g]Proportion of tert- <1 ppm  4 ppm butanol [ppm] Proportion of n-heptane  9 ppm 671 ppm [ppm]

TABLE V Comparison Example 3 Example 3′ MFR (I)/MFR (II)/ 115/7.5/7.515/3.5/7 MFR (after reduction) XS [%] 32 33 Modulus of elasticity 745613 [MPa] ack (23° C.) [kJ/m²] 59 66 ack (0° C.) [kJ/m²] 20 67 Spiralflow [cm] 74 60 Thermostability B [° C.] 67 62 Vicat A [° C.] 41 37P.I., matrix 3.52 2.78 Crossover module, matrix 35,000 39,000 [Pa] Limitviscosity rubber 4.68 dl/g 2.68 dl/g [^(n) _(rubber), dl/g] Proportionof tert- <1 ppm    15 ppm butanol [ppm] Proportion of n-heptane 36ppm >500 ppm [ppm]

1. Highly flowable propylene block copolymers, comprising 50 to 80 wt.-%of a propylene homopolymer and 20 to 50 wt.-% of a propylene copolymer,with 10 to 70 wt.-% of a C₂-C₈ 1-alkene other than propylene polymerizedinto it, this 1-alkene being obtainable by two-stage polymerization bymeans of a Ziegler-Natta catalyst system from the gas phase; in a firstpolymerization stage, propylene is polymerized at a pressure of 10 to 50bar, a temperature of 50 to 100° C., and a mean dwell time of thereaction mixture of 0.3 to 5 hours in the presence of at least 2.0vol.-% of hydrogen in proportion to the total volume, and then thepropylene homopolymer obtained in the first polymerization stage isintroduced along with the Ziegler-Natta catalyst system into anintermediate container, where it is first depressurized for 0.1 to 5minutes to less than 5 bar and maintained at a temperature of 10 to 80°C., and then, by the introduction under pressure of a gas mixture, thepressure in the intermediate container is raised again by 5 to 60 bar,and the propylene homopolymer along with the Ziegler-Natta catalystsystem is thereupon transferred to a second polymerization stage, wherea mixture of propylene and a C₂-C₈ 1-alkene is added by polymerizationto the propylene homopolymer at a pressure of 10 to 50 bar, atemperature of 50 to 100° C., and a mean dwell time of 0.5 to 5 hours,and the weight ratio between the monomers converted in the first andsecond polymerization stages, respectively, is adjusted to be in therange of 4:1 to 1:1.
 2. The highly flowable propylene block copolymersof claim 1, wherein their melt flow rate (MFR), at 230° C. and at aweight of 2.16 kg, measured by ISO standard 1133, obeys the followingequation (I):MFR≧101.39+0.0787*XS ²−5.4674*XS,   (I) in which XS stands for theproportion of the propylene in percent, refer to the total propyleneblock copolymer.
 3. The highly flowable propylene block copolymers ofclaim 1 or 2, wherein besides a titanium-containing solid componentwhich among other components contains a halogen-containing magnesiumcompound, an electron donor, and an inorganic oxide as a vehicle, theZiegler-Natta catalyst system used also has an aluminum compound and afurther electron donor compound.
 4. The highly flowable propylene blockcopolymers of claims 1-3, wherein in the first polymerization stage,propylene is polymerized at a pressure of 15 to 40 bar and at atemperature of 60 to 90° C.
 5. The highly flowable propylene blockcopolymers of claims 1-4, wherein, per kg of the propylene homopolymerin the intermediate container, 0.001 to 10 g, refer to the propylenehomopolymer, of a C₁-C₈ alkanol is added.
 6. The highly flowablepropylene block copolymers of claims 1-5, wherein in the intermediatecontainer after the depressurization, the pressure is raised again byfrom 10 to 40 bar by introducing a gas mixture under pressure.
 7. Thehighly flowable propylene block copolymers of claims 1-6, wherein in thesecond polymerization stage, a mixture of propylene and a C₂-C₈ 1-alkeneare polymerized with one another at a pressure of 10 to 40 bar and at atemperature of 60 to 90° C.
 8. A method for producing highly flowablepropylene block copolymers of claims 1-7, by two-stage polymerization bymeans of a Ziegler-Natta catalyst system from the gas phase,characterized in that in a first polymerization stage, propylene ispolymerized at a pressure of 10 to 50 bar, a temperature of 50 to 100°C., and a mean dwell time of the reaction mixture of 0.3 to 5 hours inthe presence of at least 2.0 vol.-% of hydrogen in proportion to thetotal volume, and then the propylene homopolymer obtained in the firstpolymerization stage is introduced along with the Ziegler-Natta catalystsystem into an intermediate container, where it is first depressurizedfor 0.1 to 5 minutes to less than 5 bar and maintained at a temperatureof 10 to 80° C., and after that, by the introduction under pressure of agas mixture, the pressure in the intermediate container is raised againby 5 to 60 bar, and the propylene homopolymer along with theZiegler-Natta catalyst system is thereupon transferred to a secondpolymerization stage, where a mixture of propylene and a C₂-C₈ 1-alkeneis added by polymerization to the propylene homopolymer at a pressure of10 to 50 bar, a temperature of 50 to 100° C., and a mean dwell time of0.5 to 5 hours, and the weight ratio between the monomers converted inthe first and second polymerization stages, respectively, is adjusted tobe in the range of 4:1 to 1:1.
 9. Use of the highly flowable propyleneblock copolymers of claims 1-7 for producing films, fibers or moldedbodies.
 10. Films, fibers and molded bodies containing highly flowablepropylene block copolymers of claims 1-7.